1. Field of the Invention
The present invention relates to providing a robust error recovery due to data losses incurred during transmission of signals. More particularly, the present invention relates to a method of transformation of data to explicitly transmit control information.
2. Art Background
A number of techniques exist for reconstructing lost data due to random errors that occur during signal transmission or storage. However, these techniques cannot handle the loss of consecutive packets of data. Consecutive loss of packets of data is described in the art as burst error. Burst errors result in a reconstructed signal with such a degraded quality that it is easily apparent to the end user. Additionally, compression methodologies used to facilitate high speed communications compound the signal degradation caused by burst errors, thus adding to the degradation of the reconstructed signal. Examples of burst error loss affecting transmitted and/or stored signals may be seen in high definition television (xe2x80x9cHDTVxe2x80x9d) signals, mobile telecommunication applications, as well as video storage technologies including video disk and VCRs.
For example, the advent of HDTV has led to television systems with a much higher resolution than the current standards proposed by the National Television Systems Committee (xe2x80x9cNTSCxe2x80x9d). Proposed HDTV signals are predominantly digital. Accordingly, when a color television signal is converted for digital use it is common that the luminance and chrominance signals may be digitized using eight bits. Digital transmission of NTSC color television signals may require a nominal bit rate of about two-hundred and sixteen megabits per second. The transmission rate is greater for HDTV, which may nominally require about 1200 megabits per second. Such high transmission rates may be well beyond the bandwidths supported by current wireless standards. Accordingly, an efficient compression methodology is required.
Compression methodologies also play an important role in mobile telecommunication applications. Typically, packets of data are communicated between remote terminals in mobile telecommunication applications. The limited number of transmission channels in mobile communications requires an effective compression methodology prior to the transmission of packets. A number of compression techniques are available to facilitate high transmission rates.
Adaptive Dynamic Range Coding (xe2x80x9cADRCxe2x80x9d) and Discrete Cosine Transform (xe2x80x9cDCTxe2x80x9d) coding provide image compression techniques known in the art. Both techniques take advantage of the local correlation within an image to achieve a high compression ratio. However, an efficient compression algorithm may result in compounded error propagation because errors in an encoded signal are more prominent when subsequently decoded. This error multiplication may result in a degraded video image that is readily apparent to the user.
In the ADRC process, for example, the image to be compressed is divided into disjoint sets of pixels called blocks. Information can then be transmitted in a block by block manner. For each block, a minimum pixel level and maximum pixel level are determined. The range of pixel values between the minimum and maximum level, referred to herein as the dynamic range (DR), is then divided into equally sized sections, referred to herein as quantization bins. Thus the number of bins is variable. If the dynamic range is divided into 2Q quantization bins, the transmission of the approximate pixel values is referred to as Q bit quantization.
Each pixel in the block is approximately transmitted to the decoder based on which of the quantization bins it falls into. The number of the quantization bin the pixel falls into is the Qcode for the pixel. The Qcode is subsequently provided to a decoder can approximate the pixel value using block control information and the Qcode. The control information, also referred to herein as fixed length data, includes the number of quantization bins, the minimum pixel value and dynamic range of the block. Decoding becomes quite difficult if the block control information is lost during transmission to the decoder. In certain instances, the lost block control information can be reconstructed at the decoder. For example, the control information typically transmitted with an encoded block of data includes the dynamic range, motion flag and the minimum value or maximum value or central value. Q is not typically transmitted to save on the required number of bits transmitted as Q is determined from the dynamic range in the same way that the encoder determines Q. However, if the dynamic range is lost, Q can not be determined in a straightforward manner. Typically, in such cases, Q is estimated using available information.
One solution to this problem is to explicitly transmit the Q value for each block. However, it is desirable to minimize the number of bits transmitted in the encoded bitstream.
The present invention includes a system and method that explicitly transmits at least one block attribute as part of the encoded data without adding bits to the encoded bitstream. In one embodiment, the block attribute is explicitly transmitted as part of the encoded data, located at determined bit locations of the encoded data. The bits in these determined positions are transformed so that they correspond to the value of a particular block attribute. In one embodiment, these bits are set to equal the block length. A decoder can therefore read the block attribute directly from the bitstream. In order to transmit the bits in the determined bit locations, the previous values of these bits must be overwritten. To recover these original bits, in one embodiment, the encoder performs a transformation on the remaining bits in the block which allows the decoder to recover the original bits that were over-written by block attribute data.